Abstract
The foodborne bacterial pathogen, Campylobacter jejuni, possesses an N-linked protein glycosylation (pgl) pathway involved in adding conserved heptasaccharides to asparagine-containing motifs of >60 proteins, and releasing the same glycan into its periplasm as free oligosaccharides. In this study, comparative genomics of all 30 fully sequenced Campylobacter taxa revealed conserved pgl gene clusters in all but one species. Structural, phylogenetic and immunological studies showed that the N-glycosylation systems can be divided into two major groups. Group I includes all thermotolerant taxa, capable of growth at the higher body temperatures of birds, and produce the C. jejuni-like glycans. Within group I, the niche-adapted C. lari subgroup contain the smallest genomes among the epsilonproteobacteria, and are unable to glucosylate their pgl pathway glycans potentially reminiscent of the glucosyltransferase regression observed in the O-glycosylation system of Neisseria species. The nonthermotolerant Campylobacters, which inhabit a variety of hosts and niches, comprise group II and produce an unexpected diversity of N-glycan structures varying in length and composition. This includes the human gut commensal, C. hominis, which produces at least four different N-glycan structures, akin to the surface carbohydrate diversity observed in the well-studied commensal, Bacteroides. Both group I and II glycans are immunogenic and cell surface exposed, making these structures attractive targets for vaccine design and diagnostics.
Highlights
In eukaryotes, glycosylated proteins are ubiquitous components of extracellular matrices and cellular surfaces
Phylogenetic comparisons showed that campylobacters divide into two major groups that comprise the thermotolerant and the nonthermotolerant species with C. lari and related species forming a subgroup, within group I (Fig. 1)
No reactivity against proteins from the group II species was observed suggesting that these organisms are either incapable of synthesizing N-glycans or they produce different oligosaccharide structures compared with C. jejuni
Summary
NCTC: National Collection of Type Cultures; CCUG: Culture Collection, University of Göteborg, Sweden; LMG: Belgian coordinated collection of microorganisms; ATCC: American Type Culture Collection. A unique array of glycosyltransferases, which correlate with their phylogenetic relatedness
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